PARSIPPANY -- The great building stands atop a hill, overlooking a magnificent tree-lined avenue here.. With marble pillars, a rotunda, beautiful interior staircases and high ceilings, the massive 133-year-old structure is like nothing else in Morris County.

Greystone Park Psychiatric Hospital was the centerpiece of "enlightened’’ psychiatric facility dating to 1876, home to thousands of patients and many more thousands of workers. It has been prominent in the history of Morris County and the state for parts of three centuries.

Robert Sciarrino/The Star-LedgerA 2004 file photo of the now abandoned old Greystone Psychiatric Hospital building. The massive structure is not on any state or national historic registers, but a grassroots movement is starting to call attention to its history and get it registered and preserved.

Yet, the nearly half-million square-foot structure, with the biggest footprint of a building in the U.S. prior to construction of the Pentagon, is not officially historic.

The now-abandoned and mothballed Greystone, which is on Morris County’s and Preservation New Jersey’s endangered historic sites lists, has never been enrolled on the state and/or national historic registers — an omission a current group of preservationists hope to correct.

"Is it above the line of importance to make it eligible for the register? You bet,’’ said Marion Harris, head of the Morris County Trust for Historic Preservation and founding trustee of a new group, Preserve Greystone, that aims to save the old structure.

"It has great architectural and social significance. No question of its value,’’ she said.

Getting Greystone on historic registers could help prevent demolition or changes to its historical integrity. It also would make it eligible for state and county preservation dollars, federal tax credits and other benefits, said preservationists, who fear the cash-strapped state only sees potential profits if it could be sold to a developer.

Designed a few years after the Civil War by Philadelphia architect Samuel Sloan, Greystone is a French Renaissance/Second Empire style building. It is an example of the Kirkbride plan, espoused by Thomas Kirkbride, one of the most influential physicians in the care of the mentally ill in the United States in the 1800s.

Kirkbride’s sought benevolent settings for patients. Every window in the hospital had a view of the surrounding countryside. Fresh air and circulation were ensured through architecture. There were striking reception and visiting areas, and a beautiful chapel for worship. His design included a pastoral setting, providing a means of treatment through privacy and allowing activities such as farming, gardening and exercise at the hospital.

Robert Sciarrino/The Star-LedgerA 2006 file photo of the staircase and Minton tiled floor located in old Greystone Psychiatric Hospital building.

"It is historically and architecturally significant. And it is an amazing community landmark," said Ron Emrich, executive director of non-profit Preservation New Jersey. "It has a significant story to tell about generations of people who lived and worked there.’’

Getting it listed on the historic registers could help save it and be a boon to any future re-development or rehabilitation effort, whether done by a public or non-profit entity, private business or a public-private partnership.

"The benefits can be substantial,’’ said historic architect Margaret Westfield, whose Drew University historical properties class a decade ago unsuccessfully sought to enroll Greystone on the historic registers.

Included could be grants of up to 75 percent of costs of planning and design for a proposed re-use project, and up to 50 percent of costs of rehabilitation from the Garden State Historic Preservation Trust, said Westfield. Also, private developers could get a federal investment tax credit of up to 20 percent of the cost of renovations, she said.

Harris said Preserve Greystone sought a grant from New Jersey Historic Trust to finance hiring a consultant to start the process of getting the building on the register. But the old Greystone’s current owner, the state Treasury Department, declined to sign off on the application, dooming the request.

Treasury spokesman Thomas Vincz strongly denied that contention, and said the agency has "worked diligently’’ with many stakeholders on the future of Greystone and the surrounding land.

Dorothy Guzzo, executive director of the New Jersey Historic Trust, confirmed Preserve Greystone applied for a grant but said it was not approved because the group did not yet have non-profit designation nor a required sign off by the property owner, namely Treasury.

It is up to Gov.-elect Chris Christie’s administration to reconsider the issue next year, said preservationists, who want the state to be a leader in saving this piece of its history.

"Kirkbride had a remarkable idea and he brought it to life,’’ said Randy Tortorello, town historian for Parsippany. "We have an obligation to try and save it.’’